Epeorus (Caucasiron) turcicus sp. nov. is described based on larvae from NE Turkey. The new species can be distinguished from other Caucasiron by a unique combination of several diagnostic characters: the presence of a rounded hypodermal medial femur spot, colouration of abdominal terga and sterna, narrow gill plate VII, fine hair-like setae on the surface of abdominal terga, and absence of postero-lateral projections on tergum X. In addition to morphological analysis, two single-locus analytical approaches are employed for delimiting the new species using COI sequences (Automatic Barcode Gap Discovery, ABGD; and General Mixed Yule Coalescent Model, GMYC). Both approaches unambiguously recognized E. (C.) turcicus sp. nov. as a distinct species. Our molecular dataset contains all Caucasiron species occurring in the Caucasus and the delimitation of individual species mostly follows the morphologically defined species. This study confirms the suitability of the GMYC approach for species delimitation within Caucasiron.

As part of our detailed study of the Caucasian mayfly fauna, we describe Epeorus (Caucasiron) abditussp. nov., a new species of the genus Epeorus Eaton, 1881, subgenus Caucasiron Kluge, 1997, based on larvae collected in Türkiye, Georgia, and Russia. We use several methodological approaches to delimit the new species by analysing COI sequence data and larval morphology. We provide a comparison with related taxa and diagnostic characters allowing determination of the larvae. We also update the identification key for the Caucasian species of E. (Caucasiron) with E. (C.) abditussp. nov. and two recently described species, E. (C.) hyrcanicus Hrivniak & Sroka, 2021 and E. (C.) tripertitus Hrivniak & Sroka, 2022.

In this study, we aimed to determine the reference sites and their reference Ephemeroptera communities according to the Water Framework Directive methods in the Eastern Part of the Black Sea Region of Turkey between 2008-2011. From the area, twentyfour collecting sites were chosen. There were thirty Ephemeroptera species identified, belonging to seven families and eleven genres. Cluster analysis based on Bray-Curtis similarities was applied. Reference habitat conditions of the studied sites and their reference Ephemeroptera communities were determined by combining both ecological and statistical results. As a result, sixteen sites had reference habitat conditions and their reference Ephemeroptera species were identified.